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Does the Fairchild Metroliner have any unusual handling characteristics?
I have been told by several people that the Fairchild Metroliner is a quite difficult to handle aircraft.
Aside from that, I have seen that it has suffered several accidents throughout its history.
Does it have any aerodynamic deficiencies in its design or something like that?

Your question is basically asking for opinions. That said, I'll give you mine plus a bit of objective information. I flew SA-226 and SA-227 Metroliners for about two years, commuter flying (4 to 8 legs a day), mostly in U.S. Pacific Northwest weather, two pilots, no autopilot.
The Metroliner was considered by many to be a high workload, unforgiving aircraft. See this for more on that, but I did not find it unreasonably so. However, anytime you have a high work load, fast aircraft, the potential for incidents/accidents gets a little greater than if either of those things is not true.
It was not an airplane that you could get consistently good landings in if you consider a good landing one that is smooth (whatever that means). Clunkers greatly outnumbered greasers, at least for me. The tires were small and hard, and in my opinion the long landing gear magnified clunkers. You could increase your chances of a greaser by carrying a lot of power onto the runway, but that used a lot of runway.
Nose wheel steering was hydraulically actuated via the rudder pedals. It was not uncommon for the system to be inoperative, and the aircraft could be dispatched without it, in which case you had a castoring nose wheel. New captains dreaded being dispatched with inoperative nose wheel steering. Once you got used to it though, it was no problem. In fact, if you had to do some really fancy maneuvering on the ramp, you could turn off the nose wheel steering and if need be pivot about a main gear.
Far from any aerodynamic deficiency, at least in my opinion, it was great in that respect in that it was fast, but had the ability to slow down quickly.
Controllers liked it (and took advantage of this) that it could fly at jetliner approach speeds from the outer marker inbound until short final. Controllers at SFO would often put us between jetliners going down final, or from a left downwind for 28L clear us from that downwind for an asap short final knowing that we could do it. We would touch down beyond where the jetliners did but still in time to make the turnoff to what was then the commuter ramp. When you dropped the gear and flaps and brought the props back to an almost flat pitch with no power, it quickly slowed and/or came down.

How do you steer the aircraft during taxi without the nose wheel? Differential braking?

@HenningMakholm - (Guessing from the pictures) Possibly differential power between the two engines? If the propeller pitch allows reverse thrust, it could theoretically rotate around the center of mass?

@HenningMakholm Speaking for myself, whether in a Metro with the nose wheel steering inop or any aircraft with a freely castoring nose wheel, I used differential breaking for straight line tracking. In a turn,if it's a multi-engine aircraft, I typically used additional power on the engine to the outside of a turn to help it around, just as I would when operating a multi-engine aircraft with operative nose wheel steering if it was a sharp turn.

The data indicates that it is a challenging airplane relative to the Beech 1900, its closest competitor.  Looking at hull loss events, or events in which the plane is destroyed beyond repair, here is what I see...
The Beech 1900 has had 41 hull losses since 1982, or 1.17 per year.
The Metro and Merlin IV (including the Merlin IV because it is often used in the same capacity as the Metro) have had 108 and 19 hull losses, respectively, for a combined total of 2.65 per year.  That's over 2x the rate of the 1900.
Now, why that rate is >2x higher than the 1900 is another question.  I don't think it's a design deficiency.  The problem is the pilot.  The Metro has been used in the freight business for some time which is a dark corner of the aviation industry known for playing a little fast and loose with the rules.  Combine the lax attitude of the freight world with bargain basement maintenance and add a plane that is not quite as docile as airplanes that pilots had flown previously, like Navajos and Twin Cessnas, and you get a turboprop with a reputation!  Keep in mind that freight operators will upgrade pilots from piston twins directly into the left seat of a Metro and send them off single pilot.  That was my path.  Was it dangerous?  Probably.  But, as the meme goes: did you die?  No...and who says no to a free type rating and turbine PIC, right?
The Metro is challenging to fly and it does punish pilots who become complacent.  It also yaws very aggressively during V1 cuts and it will roll over if the pilot is indecisive on the control inputs.

A V1 cut requires an immediate and decisive response.
The nose wheel steering will take the plane off the runway if used improperly.  If the pilot lands with nose wheel steering
engaged and the rudder pedals cocked to one side, the nose
wheel will touch down and steer the plane off the runway before the
pilot figures out what happened. I know two pilots who have done
this and was #1 in trail of one of them.  Popped out of the clouds on an ILS and there's a Metro off the side of the runway in the snow!
The propellers do not have auto-feather.  They use a system called negative torque sensing (NTS).  NTS is a system that senses a
scenario in which the airflow drives the engine via the propeller
instead of the engine driving the propeller.  The NTS  says, "oh, the
engine is not turning the propeller...the engine must have failed,"
and the propeller tries to feather.  As it feathers, another system
says, "no, not yet..." and drives the propeller back to low pitch. This
feels like pulses to the pilot, about one per second.  If NTS fails
and an engine quits, the propeller will not try to feather and the
plane will roll over very quickly.
The fuel control unit on the engines used to be a problem.  If the FCU failed, it would fail open and let fuel flow unmetered into the engine.  This is a bad thing.  There was at least one accident in which an FCU failed and allowed fuel to flow unchecked into the engine which caused to engine to produce a lot more power than it normally would.  The asymmetrical thrust (one engine at 100% and the other at ~150%, for example) feels like a yawing motion.  This yawing motion is an indicator of a failed engine, and normally the plane yaws towards the dead engine.  Pilots would respond instinctively by identifying the failed engine (the one in the direction of the yaw) and shutting it down.  In this case, the engine shut down would be the properly operating engine. The yawing motion was caused by unregulated fuel flow into the engine causing it to surge and produce more thrust than the other engine.  Shortly thereafter, the engine with the failed FCU over-temped and/or over-torqued and destroyed itself.  The pilot, having already shut down the good engine, could not restart the engine in time and crashed.  If I recall, a pilot survived and relayed the chain of events to investigators who then looked into the FCU.  Who knows how many fatal accidents occurred prior to this accident in which nobody though to look at an FCU that failed open?

For context, I flew the Metro single pilot in the Rockies and Western Plains for a couple years, also no autopilot (virtual high five, Terry).  I've never actually seen a Metro with an IFR GPS or autopilot.  Do they exist?

Do we have a NTS vs autofeather question on this Stack? I'm curious about the difference...

I can't find one.  Basically, auto-feather will drive a propeller to a feathered position automatically.  NTS uses a piezoelectric sensor on the shaft to detect when the prop is driving the engine (the "negative torque" part) and begins driving the prop to feather but "bumps" against the governor which causes the pulsing sensation as the prop is pushed back to low pitch.  NTS requires the pilot to take the final step of actually commanding a stop/feather of the engine; it will not completely feather on its own and will pulse along all day until the pilot either adds power or feathers.

Great answer! Wish I could give more than only one upvote.

The statistics is somewhat unfair to the Metro, because while the production number is similar, it has about 10 more years in service. Good statistics would be normalised to total number of hours across the fleet, but ASN does not have that number and I don't know where to find it (at least approximately).

Also the statistics should filter out the accidents that where the cause had nothing to do with the aircraft itself (trying to land below minima is equally bad decision no matter what you fly), but that would have to be hand-counted as ASN does not seem to qualify this. Still, the difference is rather big and in a small sample I tried technical issues seemed to be well represented.

Gotta love the San Antonio Sewer Pipe!

Yes, that sounds about like what I’ve heard of the ‘San Antonio Sewer Pipe’s’ negative handling qualities.  Was not aware of the sensitive nose wheel steering. And I wasn’t aware that they did not have autopilots, either.  Maybe the Fairchild Merlin executive versions of this aircraft had them.


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What additional functionality is provided by the F-14 nose pitot, absent in early models?
Early model F-14A had no nose pitot:

... but they seem to have quickly acquired them sometime in the late 1970s. The Iranian F-14s have them, and it's quite hard to find a picture of an F-14 without a nose pitot.
This is the nose pitot that appears on the majority of F-14s:

I believe the nose pitot measures angle of attack, a measurement I would have thought was critical to a big carrier-based aircraft like the F-14 from the outset.
So, why were the nose pitots introduced, and what effect did it have on the nature of piloting an F-14?

It might help to provide a picture that specifically shows the feature you're asking about, or mark it on the ones above (please also provide your image sources, by the way). A pitot tube and an angle of attack vane are different things, and it isn't clear to me exactly what you're looking at.

done and done, thanks.

The probe on the nose isn't a pitot tube (although it might looks like one).
That's an AoA sensor as explained here: Home of M.A.T.S. - Sensor Probes
Reported from the link above:

Angle-of-Attack Nose Probe: The Angle-of-Attack (AOA) is an essential dimension since it measures the angle between the aircraft's vertical flight direction and the vertical wind direction. A too high AOA means that at a given speed the wings will fail to produce lift which will result in a loss of controllability and stability. This is especially important during the landing phase where the aircraft is fairly slow approaching the carrier and also during air combat maneuvering where a loss of controllability can be deadly.
   Each AOA probe measures the pressure at several points and then the AOA is calculated. Usually, several AOA probes are installed to measure a correct AOA.
   Note that this probe was not installed on very early F-14As

The same site, on a related page, report what you've alredy found:

The first fleet Tomcats were not equipped with any nose probe, but todays F-14s carry a small nose probe to gather air pressure data to calculate the angle-of-attack

Thanks - the part I'm struggling to understand is how an aircraft like the F-14 coped without an AoA sensor; or, if it had one (presumably it did), why was there a need for a newer one?

@PartyArk, if you open the first link, sensors referenced by points 3 and 5 are also AoA sensors, so even early F-14s already had not one but two AoA sensors. :-)

Thanks, I see that, but I'm still not sure why they felt the need to introduce an extra one?

@PartyArk: Extra redundancy, perhaps?

The probes numbered 3 are also labeled "AIC", which is indicated as standing for "Air Inlet Control" and apparently are involved in adjusting the position of air inlet ramps. It's possible data from those probes aren't available to the pilots though I don't really know why that would be done. I don't know what difference there might be between 5 and 1 though.

Now I am wondering how that probe works. Normally an AoA probe is either a vane—which obviously needs to be on the side—or several pressure sensors around a curved wing leading edge. I have trouble understanding on what principle a pointy sensor could measure AoA (as opposed to dynamic pressure, which is then converted to equivalent airspeed).

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Does an autopilot that controls roll, pitch and a yaw damper meet the requirements of 135.105(c)(1)?
For single-pilot VFR operations, 14 CFR 135.105(c)(1) requires that:

The autopilot is capable of operating the aircraft controls to
  maintain flight and maneuver it about the three axes

Does this mean an autopilot with roll, pitch, and a yaw damper would qualify?

Airplanes with yaw damper systems have 2 axis autopilots.  That talks about an autopilot with control about the 3 axes, so I might interpret that as a 3 axis autopilot requirement.  Yaw damper systems have very limited yaw authority (about a third of rudder travel) and perhaps that's insufficient for single pilot IFR because the rudder channel needs to be able to cope with asymmetric power/thrust, which a yaw damper doesn't have to deal with.

Looking around a bit, single pilot jets like the Phenom 300 have 2 axis autopilots with yaw dampers so it would seem the answer is yes.

I am ignorant of the rules for part 135. Can a Phenom 300, or any of the turbine aircraft, be flown single pilot outside of part 91?  Bear in mind these aircraft fly ain the flight levels normally, thus IFR.

The Phenom 300 is single-pilot certified so the autopilot requirement is moot.

Multi Axis Autopilot
Multi Axis Autopilot is a system which controls an aircraft about the roll and pitch axis (two axis) or roll, pitch and yaw (three axis). Sometimes the rudder has an independent yaw damper incorporated but this is not considered one of the axes in the system.
For aircraft with yaw damper - rudder displacement is provided by a command signal derived by cross feeding the roll angle signal from a vertical gyro to a turn co-ordination high pass filter.
The purpose of yaw damper is to improve the airplane's directional stability and ride quality. The yaw damper system is independent, but still part of the wider autopilot system. However, it can be operated independently in manual flight to correct Dutch Roll tendencies.
Yaw damper is not considered a full authority rudder channel in Automatic Flight Control Systems, meaning it isn't included as one of the axes when defining the type of autopilot. Both 2 and 3 axis autopilots can include a yaw damper system.

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Why do aviation careers have age limits?
Many aviation careers have mandatory retirement ages.

Airline Pilot (licensed with FAA): 65 (raised from age 60 a few years ago)
Controller

FAA: 56
NATS: 60

Why do these age limits exist? Is it a matter of increasing risk (even when one is healthy) of becoming incapacitated while on the job (heart-atack, etc.)?

FYI, NATS says there is no age limit for controllers

I'm no expert, but I can think of two general reasons: risk of incapacitation, and general physical limitations (reaction speed, stamina, the ability to maintain concentration for extended periods etc.). The age 65 limit only applies to part 121 ATP pilots, by the way; you can still be a commercial or private pilot for as long as you can keep getting a valid medical.
Older people are simply at greater risk of heart attacks and many other medical conditions, and they're also much more likely to require medication that may not be approved by the FAA or other national authorities. Of course that doesn't mean that every older pilot is the same but I guess that the FAA has decided that since the risks increase with age, at some point they become unacceptable. To understand the specific reasons for that decision you would probably need to dig up the original NPRM or transcripts of the public debate/hearings, but I have no idea if that's possible or not.
Then the other aspect is general physical and mental condition. They both deteriorate with age, and the NTSB sometimes mentions that as a potential factor in accidents:

On the day of the accident, the pilot had flown several formation
  sorties. The day was hot, and the formation activities were demanding.
  The accident flight was relatively long, and the co-owner of the
  airplane guessed it was about 45 minutes long. Most formation sorties
  were 30 minutes or less. The accident pilot was in his early 70s and
  was by far the oldest member of the flight. Due to the pilot’s age,
  the demanding schedule, and the length of the formation sorties,
  fatigue could have been a factor, although it could not be
  conclusively determined.

Of course, any discussion like this is a generalization and I'm sure it's easy to find individual 70-year old pilots or controllers who are 'sharper' than younger ones (after all, experience counts for a lot too). But there's no escaping the overall pattern that older people in general are more prone to medical issues and less physically/mentally capable than younger ones, and at least one US court has ruled that there's no effective way to determine individual risk so a general rule is not discriminatory:

The court also concluded that ExxonMobil had established, through the
  testimony of several medical experts, that the risk of sudden
  incapacitation in flight significantly increased with age, and that
  there are no adequate means of individually testing each pilot to
  determine whether a pilot was at risk to suffer such an
  incapacitation.

I think that the last paragraph is the most telling.  They don't know how to test people for age-related increased risk factors.  My personal belief is that we should be given a proper medical examination which would actually uncover problems that would keep us from flying, and then let us fly until we can no longer pass the exam.

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What is the expected reaction of a civil airliner pilot upon an invalid request from a fighter jet?
After asking a question about the recent diversion/pirating of the Ryanair flight in Belarus (that got closed, but has a nice answer), I got to wonder about how the pilot should have had behaved in that case (fictitious situation of a flight over Lithuania, Belarusian jets requesting it to fly back to Belarus).
What are the rules for a pilot of a civil plane when they are requested by a military plane (a fighter jet) to follow them, when the plane is from another country than the airspace?
I can understand that within an organization such as NATO, a Polish plane could fly over Germany to intercept a Singaporean plane (because of NATO agreements).
From the perspective of a civil airplane pilot - does it matter? In other words my questions are:

is the pilot expected to make a decision about whether to follow a military plane at all? (= if they see a plane that requests them to do something, should they follow the requests no matter what?)
is there any consideration of the airspace? (= should the pilot take into account the place they are above?)

I would like to highlight that I am interested in the rules on how a pilot must behave (and not acts of bravery or something like that).

The fighter may be armed.  The civilian jet is not.  If you refuse to follow signals, the fighter may decide to fire a burst of gunfire across your nose so that you understand the gravity of the situation.  Or they may just shoot you.  Or maybe the fighter is unarmed or not authorized to shoot you.  Who wants to find out the hard way?

I'm with @WayneConrad -- don't argue with the guy who has a gun (missiles count as guns in this context).

@WayneConrad: This is clear, I was expecting however that there would be some regulations about how to behave when you are being accosted by a military plane.

@WoJ ICAO says we must comply, period. Whether the interception was legal or not is something to figure out on the ground, not when an armed fighter is threatening to shoot you down.

@StephenS: thanks, this is exactly what I was looking for. Where should I look for the list of regulations (I had a look at the ICAO page but the information within are very high level)

I do get what you're asking @WoJ.  I think the reason the conversation is going in another direction is because of your title.  Instead of "What is the expected reaction of a civil airliner pilot...", a better title might be "What do ICAO rules say a civil airliner pilot must do when given an order by someone in an intercepting military aircraft?"  It would be very confusing if you were to so edit this question, because that edit would change its entire character.  The best thing might be to delete this question and ask a new one.

@rclocher3: I was hoping that the sentence would have made it clear - from a purely "regulative" perspective (or, in other words, is it just tradition to follow the fighter jets because the ones who did not showed that this is not a good idea not to do so - or are there actual rules that say "a pilot MUST follow a fighter jet requests")

@WoJ list of regulations found in the ICAO Annex 2, as referenced in my answer.

The second bold part is ambiguous - is it the fighter or the civil aircraft (or both) that is outside its home airspace in this question?  If the former, then expect the country's own military to take some action, and do your best to keep out of the way!

Under ICAO regulation, pilots of civil aircraft must comply with instructions when intercepted:

The pilot-in-command of a civil aircraft, when intercepted, shall comply with the Standards in Appendix 2, Sections 2 and 3, interpreting and responding to visual signals as specified in Appendix 1, Section 2.
(ICAO Annex 2 - Rules of the Air - 3.8.2 - emphasis mine)

Appendix 2 Sections 2 and 3 outline what should be done “immediately”

2.1 An aircraft which is intercepted by another aircraft
shall immediately: …
(ICAO Annex 2 - Rules of the Air - Appendix 2, 2.1)

These actions include amongst others; following instructions from the intercepting aircraft; notifying the relevant ATSU; attempting to establish communications with the intercepting aircraft; and selecting Mode A 7700 if possible.
As far as I am aware, EASA, FAA and the majority of other regulatory or safety authorities do not vary much from ICAO - though there may be minor variations in the visual signals given by the intercepting aircraft.
For example, EASA Regulation (EU) No 923/2012 and FAA CFR § 91 concerning this seemingly restates similar information to that found in ICAO Annex 2. Furthermore, the UK CAA’s AIP, Transport Canada's Civil Aviation Directorate’s AIP and I expect many other NAAs, have no listed differences from ICAO concerning Interception of Aircraft.
From your question:

“is the pilot expected to make a decision about whether to follow a military plane at all?”

As explained above, probably not. By statute (and by common sense): obey the intercepting aircraft.

is there any consideration of the airspace?

Probably not. (Also, civil aviation flying over territory is more of an ICAO concern (United Nations) - not NATO)

If the intercept is illegal, you could expect the ATSU you notified to initiate the appropriate corrective action.

What do rules have to do with your hypothetical situation?  At that point the question is what a completely unarmed person, who is immediately responsible for the lives of other people (assuming there are passengers), should do when another person who clearly doesn't obey laws and has a deadly weapon demands something, and nobody else has the power to interfere.
It seems to me that the choices available to the civil pilot are to comply, to refuse, or to try some sort of trick.  A rational person at that moment would be completely concentrated on survival for the aviator and passengers, and wouldn't be concerned about rules.

See @StephenS comment - this is the kind of rule I was looking for. Why do you say that the situation is hypotetical?

@WoJ, but rclocher didn’t actually quote any real rule.  In fact, I interpreted the point in their answer as being that there aren’t rules for every situation in life, and that rational people need to decide the best course of action based on the situation.  Your question even specifies that it is an “invalid request”.  What “rule” would you follow if a mugger made an invalid request for your wallet?

@MichaelHall: taking a closer example - if a plane is hijjacked and there is a regulation that forces the pilot to fly to the nearest airport in case of a hijacking no matter what (people being killed in the plane for instance) then they should land at the nearest airport. Same if the police stop you even if they should not - you stop because the rules say that when a police car asks you, you do it. My question was about the existence or not of such rules. StephenS mentioned ICAO but I did not find anything on their page.

Hi @WoJ, I say that the situation is hypothetical because it hasn't happened in the modern era of air traffic control and radar, as far as I know, and your question said that it was fictitious.  If a fighter has crossed an international border to force a civil aircraft back across the border, I'd be quite interested to read about it; that would be quite a diplomatic incident.

@WoJ, my point is that there is a difference between an actual forceful and illegal commandeering of a vessel and an “invalid request”.

A regulation doesn't force anyone to do anything @WoJ, it merely prescribes penalties for doing things that it says one shouldn't do, or not doing things that it says one should.


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Is it possible to use normal headphones for passengers in a light aircraft?
I'm just finishing up my private license and am looking forward to taking some friends up in a Cessna 172.  I've invested in a nice aviation headset for myself, but, as none of my friends are pilots, they don't have headsets of their own.  Even the cheapest aviation headsets (at least that I've found) are around $100; friends going up for an occasional flight don't want to spend that kind of money, and I certainly don't want to shell out for several spare headsets.
My question is, are there adapters available so that normal headphones could be plugged into a standard 2 jack connector?  I have not been able to find any online.  While certainly not too effective at reducing noise, this would at least give my passengers some comfort and would allow me to communicate with them without shouting during these short and infrequent flights.  Worst case scenario, I could give them all earplugs, but it would definitely be helpful to have some kind of headset solution so that I'm not shouting through the sound of the prop and the earplugs and they're not shouting through my ANR.

Where are you getting your plane from?  If its a rental or club-situation, they very likely have extra headsets for loan or cheap rental.

There are some solutions to convert a normal set of headphones into an aircraft headset, but in total they are going to cost you more than a base level headset would.
One popular (available in TSO and non-TSO options) option is UFlyMike which is an adapter for Bose noise cancelling headphones that adds a microphone and connects to a standard 2 jack airplane audio panel.  But back to your issue at hand, this is not cheap.  The UFlyMike will set you back around \$200 and the Bose headphones are another \$300, making this adapted headset cost a total of \$500.  This is a bargain compared to an actual Bose aviation headset, which runs around \$1000, but is well above an entry level non-ANR headset.
Your best bet is to ebay some old clamp style headsets (e.g. DC) to get some cheap headsets and then keep around your current headset when you eventually upgrade (unless those trade-up deals from e.g. Lightspeed are too hard to resist) to build up a stock.  Alternatively, if you are renting, you may be able to rent a few headsets with the plane so everyone can be equipped for a trip.

There is a way to use ordinary headsets. It can be done like this:
This is a picture of a normal headset jack for audio.

Then you would need this (1/8 inch female to 1/4 inch male) adapter:

Using this, you can get your passengers hear you and any communications you have with ATC or other airplanes etc.

Personally, I do not like this approach. Reasons:

They cannot talk to you or reply you if you ask them anything.
Ordinary computer headsets don't reduce noise levels on an airplane.
You still need to buy an adapter which isn't commonly available at homes (like a headset).

My recommendations would be:

If you are renting the airplane, the owner might have inexpensive headsets available for you to borrow. Flight Schools have many headsets as not all students buy their own in the beginning specially.
Flying is an expensive hobby. If you can afford it, you may buy a few extra headsets for $100 each.
Ask your friends to buy their own if they want to be your frequent passengers. After all, you can taking them for a very enjoying ride without them paying you for it.

I'm not sure converting a regular set of headphones is the best solution. You need to be able to communicate effectively with your passenger and them with you, both for safety and for their comfort.
In the short term see if you could loan a set from the flight school you are training with. Long term - there seems to be some good buys on eBay, old David Clarks etc...

This answer just came up in review (almost 5 years after posting) as flagged for length and content. Although useful, it doesn't seem to answer the question and is probably better as a comment.

It is possible with the Avee microphone add-on. It is a great solution to upgrade your ANR as a aviation headset and the look is just awesome!

AUDIO

Built in acoustic noise reduction (ANR) in the headphones
Separate buttons for volume control making adjustments easy and fast
Passengers can adjust their headset volume independently from the pilots headset volume
Fully automated audio connection whether stereo or mono signal is available—no need to switch settings
Microphone output level is automatically adjusted with the option to manually adjust if required

NO CONFIGURATION REQUIRED

Complete the Avee connections with your headphones and aviation audio panel no additional setup required

FAILSAFE OPERATION

System will continue to communicate and receive audio if headset battery power is lost

NOTIFICATIONS

Status LED located on the headset will flash red to identify if a cable connection loss has occurred
Audio messages will be communicated if a cable connection is lost
When headset battery power is low audio messages will be communicated at 10% intervals starting at 30% until all battery power is lost

SYSTEM TEST FUNCTION

Ability to test all functions of the headset without connections to the aircraft
Connect your headset to your PC or Mac via USB cable

WARRANTY

3 year limited warranty for the Avee Microphone Add-ons

Welcome to aviation.SE! The link appears to be incorrectly spelt. Do you have any affiliation with the company, by the way?

That product is even more expensive than spare headsets like the OP says

Yes, it is possible to cobble together some sort of headphone system, but another consideration is whether or not these unapproved systems will damage the aircraft radio system. Audio systems are designed with certain impedance values, plugging in non-aircraft headphones could burn out the audio system. Hopefully the audio panels are robust enough to handle other headsets, but why take that chance?
FAA TSO-C139 addresses aircraft audio systems, and most aircraft headsets meet that specification. There continues to be confusion about aircraft headsets that do not meet that specification, especially in air transport where pilots can bring their own non-approved headsets into the cockpit.
My recommendation is to buy, borrow or rent the approved headsets for aircraft. If you bring back an airplane that was damaged because of plugging in the wrong headsets, you would have been better off just buying an inexpensive approved headset.

There is another good solution to convert a consumer ANR headset like the Bose NC 700 for use in Aviation: AvMike.
It's something like 180 EUR, so not too much cheaper that the already suggested UFlyMike, but especially for people living in Europe probably quicker/cheaper to get. Furthermore, AvMike supports more headset brands (not just Bose).
For the question why it's so expensive although it's "only" an adapter:
The main challenge using consumer headsets in aviation is the required impedance converter to allow it to be used with the aircraft intercom system. That drives the price obviously as it's not just a "simple adapter" after all.
Still you are able to get a very decent ANR headset for aviation this way for less than half of e. g. a Bose A20 would cost you.

I did some brief searching and couldn't find any adapters, although there are plenty for the  other direction, i.e. to use an aviation headset with a PC.
But in any case, using a regular headset would probably be a bad idea, even for short, infrequent flights. The issues are sound quality, lack of a microphone, and poor hearing protection.
First, you want to make sure that your passengers can hear you clearly for safety reasons. If you have to make an emergency briefing or ask them to assist you for any reason then you need to be sure that they can understand you immediately.
Second, you want to be able to hear your passengers so they should have usable microphones. I always brief mine to tell me about aircraft they see that I haven't already pointed out: I can't see everywhere and using my passengers as spotters is really helpful, but it won't work if I can't hear them.
Finally, aviation headsets protect your ears - either actively or passively - from the relatively loud background noise in the cabin. Normal headsets don't do this very well and certainly not well enough for a light aircraft cabin, so your passengers will probably end up feeling somewhat deafened and uncomfortable, which isn't good for anyone and means they'll be less likely to fly with you again.
I think the best thing you can do is just look for some cheap headsets. I've had one pair for 8 years and they still work just fine so the cost over the long term isn't so bad, although of course I know it can still be a big hit up front. \$100 isn't much at all when you consider the benefit you get from it. Alternatively most FBOs will rent you headsets for a few dollars per flight, but even then you can spend \$100 fairly quickly.

Today, I took a \$300-\$400 (depending on sale) Bose 700 consumer headset into a Vans RV6A with the Lycoming O-360.  I compared it in the same airplane to a Lightspeed Sierra $650 ANR headset whilst engine running.  This is not a gimme comparison.  The Sierra is very good.
The Bose 700 was definitely not any worse than the Lightspeed on headphone noise cancellation.  The 700 does have a smaller ear cavity, it seems more fragile, and by the time one adds one of the $250 aviation-adapter microphone to it, it costs the same.  But it is not an inferior hearing solution and it is lighter and more comfortable.
YMMV.
I do wonder why no one has a cable or Blutooth adapter that just uses the built-in MIC on consumer headsets.  (Now the MIC may not work because the ambient noise is very loud.)  In any case, \$250 seems pretty steep for a simple cable adapter and a simple MIC.  The parts are probably \$20, s/h another $20.  I could see \$100, but \$250 seems steep?  Are there any cheaper conversion solutions?

true, but the highly rated reviews suggest this is not a good idea.  I could add my post into one of them at the end to clarify instead....


text:
How does the pitching moment change as the speed of A/C approaches critical Mach number?
In an aircraft performance course, I saw that pitching moment goes backwards as the speed of A/C approaches critical Mach number. In fact, that results in nose down pitching moment. But, according to my notes, there must be shock waves at the back of the A/C. In this situation, should not these waves behave as force pitching down? How can it be possible? And why?

@mins yes that was exactly what I meant

Yes most aircraft which operate in the transonic zone experience a nose down pitch with increase in speed. The two main causes are :

Rearward movement of centre of pressure
Because of supersonic acceleration at higher speed, pressure continues to decrease past the 50% chord point, thus increasing the amount of lift produced by mid chord part of wing.
Modification to airflow over the tailplane
Most tailplane work in a region of downwash from the mainplane, in case of swept aircraft the downwash can be considerable. The formation of shockwave on main plane modifies the flow such that the downwash is reduced and this will pitch aircraft nose down


text:
During single-engine taxi, how is the asymmetric power compensated for?
For various reasons (e.g. noise, fuel savings), some airlines allow single engine taxiing. Obviously, this produces an asymmetric thrust during the taxi. If the left engine is used, the aircraft always wants to steer to the right. How is this compensated? Do pilots use the tiller all the time to countersteer, or pedals, or brakes? Is there a possibility to "trim" the aircraft during taxiing?

There will be more force on the tiller (if the tiller has feedback), but if the tiller is straight the aircraft should go straight too.

I find this question interesting. In about 1978 I shutdown my single engine recip for an exceptional long delay (about 15min). Later I received a reprimand from the control tower and was given a FAR that prohibits aircraft from shutting down an aircraft engine while maneuvering on an airport. I looked for this FAR for this answer but was unable to find it. Apparently their is a difference between jets or at least multi-engine aircraft. Or, the FAR's have changed. A google search showed multi-engine shutdown a common practice...

The nose wheel.

@jwzumwalt Logically there may be a difference for vehicles that require a ground power unit to restart their engines...  Perhaps that might help refine your search.

I once tried a single engine taxi with a Beechcraft King Air - a twin-turboprop - in X-Plane, it was uncontrollable. Is this a feature of twin-props or a fault in the simulation?

@Christian - this is precisely part of the origin of my question, the behaviour in XPlane. I do know however that ground taxiing is poorly modeled in most flight simulators. I heard from many pilots that a lot less thrust is required in realtiy to begin taxiing...

First off, the thrust asymmetry problem is far less pronounced in large jet aircraft as compared with light twin engine propeller driven aircraft.  Secondly, taxi operations generally don’t use very much thrust, with the engines often at idle power during this process, only requiring brief bursts of moderate thrust to get the aircraft moving from standstill.
Taxiing small, light twins can be difficult in an OEI (One Engine Inoperative) scenario, in many cases being almost impossible to turn the airplane sharply toward the good engine.  Sometimes pilots will simply turn the aircraft only towards the dead engine and perform a 270° turn toward the dead engine instead of attempting to turn the airplane toward the good engine, should a turn toward the good engine be required.  Sometimes, as a loss of an engine becomes an emergency situation, a light twin pilot will sometime just shut down on the runway or on a turnoff, then just have the aircraft towed back as opposed to attempting to taxi it with an OEI.
Asymmetric thrust can also be used by light twin aircraft to perform even sharper turns at slow speeds, with the pilot simply advancing the throttle to the engine on the outside of the turn while leaving the throttle on the inside of the turn at idle.  This can also be useful for maintaining directional control while taxiing, taking off and landing in strong crosswind conditions, since it requires less rudder input to correct.

Yes.  OEI means One Engine Inoperative.

Very little thrust is required to maintain a quite adequate taxi speed. So although a small of amount of yaw is produced, it is very easily compensated for by the use of nose-gear steering.


text:
Is this plane safe to fly on? The turbine blades look damaged
While waiting for a recent flight, I observed this aircraft with what appear to be rather worn turbine blades.  Is this close to being a safety issue or is it purely cosmetic?

The pic isn't good enough to tell.   Could just be paint erosion.

@JohnK I realized later how bad the lighting was but perhaps it would be possible to turn up the contrast and see something.  It was very obvious when seen with the naked eye

Related, but not an answer. The fan (not the turbine as the title states; the turbine section is well aft and hidden from sight) is the most exposed part of the engine and suffers the most [visible] damage. As alluded to in an answer to the linked question, there are manufacturer-specified tolerances as to how far engine blades are allowed to degrade before they are considered unusable (i.e., unsafe).

@dalearn, the discolouration is very clear in the photo, but what is not clear is whether it is dirt, eroded paint, or there are actually dents in the leading edges of the blades—and I doubt it was discernible with naked eye from that distance either. Abraded paint or a little dirt are not a problem.

If Hainan is flying into arid parts of China with a lot of dust etc, the paint will get eroded off fan blades pretty fast.  The erosion can also be from ice collecting on the spinner and being shed, which gives you that random erosion pattern.

Yes, it is safe. Prior to every flight, ground technicians and one of the pilots will complete a pre-flight walk around of the aircraft, which includes checking the engines thoroughly. Any issues with the turbine blades would be noticed at this point and the flight would not depart.

Can you expand on why this particular plane is safe?  Your answer is good but it doesn’t quite address why this plane is safe to fly given the “damage” observed

@dalearn Frankly, the quality of the image you posted is not nearly good enough to be able to see any damage, if it exists.

I think the dalearn has noticed what looks like „white leading edges“ in the area between four and six o‘clock and the one near 9 o‘clock. Maybe the leading edges of all blades where initially white colored to make the fan better visible, when it was new or it‘s just reflected light. But the image quality is relatively bad.

@Peter nope, it’s definitely where the dark paint is gone.  It looked worn

Not all countries are created equal. What you say might be true if you were to fly with American or European airlines. I cannot give the same guarantee if you happen to fly with airlines that are banned from Europe due to safety issue.

@vasin1987 That's a Hainan livery; as far as I know they are not banned from EU or US airspace.


text:
Why were DHL611 and Bashkirian 2937 on a collision course?
This is about the crash over Lake Constanz/Überlingen on July 1, 2002. The planes were on a collision course, the automated TCAS told one to climb and the other to descend, but air traffic control gave the opposite order to the Russian plane and they crashed.
My question is, why were they on a collision course? I have not seen anything indicating they were off course. Don't planes flying different directions fly at different altitudes? And aren't there paths in the sky that planes are supposed to stay in?
What about flight plans? Does anyone check to see if two planes are on a collision course?

I wouldn't say that They were on a collision course before then.

@SMSvonderTann then why was a TCAS RA issued?

Did you see the Deadly Crossroads episode of the Mayday series also known as Air Crash Investigation? I believe the problem was congested airspace around an airport.

@fooot I know that, but it is hard to say that they were exactly on a collision course where they were originally.

They weren't on a collision course until they were too close. The 2 planes were at the same FL but the controller had problems with the screens and telephones and couldn't advise them. He had also a lot traffic to control and he was alone. The pilots heared the TCAS warning but followed the wrong instructions of ATC and crashed

@kepler22b Only the Russian aircraft didn't follow the TCAS.

The Airways that the planes fly on criss-cross the sky and there are many, many intersections where there can be a potential for 2 aircraft to meet.
So yes, it is normal that aircraft are routinely flight planned to be on "collision courses". The flight plans don't keep aircraft separated. They are used so that Air Traffic Controllers can know the exact routing and plan where any conflicts may occur. It is normal and safe as ATC can then keep the aircraft separated using radar.
Generally aircraft flying eastbound fly at odd altitudes and westbound aircraft fly at even altitudes. This works quite well but we can still have 2 westbound aircraft both flying at 36,000' on a "collision course" because westbound can mean any track from 180 degrees to 359 degrees.
In this case the 2 aircraft were crossing paths at about 90 degrees to each other at the same altitude.
Normally they would be constantly monitored and the ATC controller would simply have one aircraft climb or descend to avoid the other aircraft. Another common practice is to tell one aircraft to turn slightly off course to avoid the other aircraft.
On this day the ATC system and the controller were both overloaded and a number of factors contributed to the controller not seeing the conflict until it was almost too late. At the last minute he told one aircraft to descend to avoid the other. This action alone would have been fine but the order was given far too late.
The Traffic Collision Avoidance System on the aircraft also saw the conflict and automatically issued an instruction for one pilot to climb while instructing the other aircraft to descend.
The controller did not know that the TCAS had also spotted the conflict and his  command to descend was contrary to the TCAS climb command. The pilot chose to follow the controller's instruction instead of following the TCAS climb instruction. The other aircraft was also following his TCAS instruction to descend so both aircraft were now descending while still on a conflicting flight path routing.
TCAS is there as a safeguard when the ATC system fails. It should always take priority over an ATC instruction.  It is clear that the ATC system failed these pilots and TCAS operated as it should.
As pilots we spend so much time following ATC instructions that I can see how it would be difficult to ignore the controller and instead follow the TCAS instruction.

The rule that TCAS should always take priority over an ATC instruction is one of the safety recommendations after that accident.

Based on an extensive analysis of TCAS II. Version 7.0 performance since 2000 performed primarily in Europe additional changes to improve the RA logic were identified. In response to a near mid air that occurred in Japan in 2001 and Mid Air that occurred in Ueberlingen, Germany near the Swiss border in July 2002, a change was made to permit additional sense reversal RAs in order to address these type of situations. If one pilot is not following the RA, then TCAS Ver 7.1 will issue a corrective RA.

Thanks. I'm surprised that there isn't more of a system to prevent crashes, or alternatively that there aren't more crashes. I suppose planes are far enough apart that the chances of an actual collision are low even if their flight paths cross.

@ttulinsky Why do we need "more of a system to prevent crashes"? We already have two systems (ATC and TCAS) and, as a result, there are almost exactly zero mid-air collisions, despite there being millions of flights a year.

Aircraft flying in different directions fly at same altitudes (FLs) at different times. If two aircraft were to to be found in the same FL at the same time, the ATC would assign different FL to atleast one of them, so as to minimize the risk.
In this case, the controller didn't notice that the two aircraft were in the same FL due to various reasons (mainly, he was concentrating on a delayed A320). From the accident investigation report:

When the TU154M crew contacted Zurich at 21:30:11 hrs for the first time and also reported the flight level, the controller did not notice that the B757-200 had reached the same flight level and that both airplanes were approaching each other at right angles. The distance between the two aircraft was still approximately 64NM. If he had noticed the situtation, he would have instructed the TU154M crew to descend to FL350.

The investigation listed this among the immediate causes of the accident:

The following immediate causes have been identified:

The imminent seperation infringement was not noticed by ATC in time. The instruction for the TU154M to descend was given at a time when the prescribed seperation to the B757-200 could not be ensured anymore.


text:
What is the noise level inside the Tu-114's passenger cabin?
Was the Tu-114 as noisy inside the passenger cabin as the Tu-95 bomber was said to be?

Perhaps not "as noisy as" due to at least some insulation that must have been installed, but by all accounts (including those of my acquaintances who flew it), Tu-114 was by far the noisiest airliner.
Wikipedia quotes the noise level in the cabin of around 110 dB. This is the level when one needs to yell to other's ear to be heard - which is about how it was.

Considering that the planes are very similar in design, I would think that the noise might be less if they have sound insulation. They are almost identical planes, and they both have counterrotating propellers. I never knew that the Tu-114 made a distinct noise compared to the bear.
Hope this helps!
Charlie :)

The Tu-114 was low-wing, and the Tu-95 high-wing. That difference may be significant with regard to the noise perceived inside the plane.


text:
Why was the Boeing 747SP unsuccessful?
Why was the 747SP not very successful with sales and longevity in service with the airlines that did purchase it?

Not quite sure, but downsizing a design tends to de-optimize the airframe from a weight perspective (much easier to add structure when upsizing than to pare away structure when downsizing) and the seat-mile operating cost numbers may have been inferior as a result, which is the main reason operators would move on from it in time.

What are you asking? Your question title is asking whether it was a success or not, then your body asks why it wasn't successful. Which is your question? If it's the first it's possibly opinion based, the second is more answerable. In any case there seems to be a decent amount of information online which explains it, what's missing from that?

It’s quite a simple question for you to understand! Why did the SP not sell very well. Did Boeing underestimate the market for such a aircraft type?

@keithjackson If you are asking why, then please amend your question title. If you are asking whether, then please amend your question text.

It just was not a great fit for the use case it was built for at the time it was released:

The Boeing 747SP was hit by the same problem that many airlines have
suffered from throughout history… rising fuel costs. The aircraft was
heavy, didn’t carry as many passengers as a normal 747 and was
expensive to run (four engines after all). Boeing had expected to
build up to 200 of these aircraft, but their dreams were never
realized.
Additionally, by the early 1980’s, other aircraft started to arrive
that could easily perform the same route and provide a better
passenger experience. The last commercial flight of the Boeing 747SP
flew in 2006 for Iran Air. As the country is currently under embargo
and spare parts cannot be flown in from Boeing, it is likely that they
retired them out of necessity, rather than just replacing them with
something better.

It was a clunky 4 engine fuel hog, which was not great with rising oil prices

The aircraft, despite its long range, was not popular with airlines,
and only 45 were built. This was mainly due to its four-engine
configuration, which meant high fuel usage and higher costs for
airlines, making it difficult to break even on ultra-long-haul
flights. Shorter flights weren’t profitable either, as the 747SP’s
high fuel capacity added weight and increased fuel burn on short hops.
The aircraft’s failure was not due to a lack of effort on the part of
airlines.


text:
Why couldn't the DHL611 crew hear the ATC transmissions for the Bashkirian 2937 crew?
In the mid-air collision over Uberlingen, why couldn't the DHL611 crew hear the instructions given by the controller to Bashkirian 2937 crew if both aircraft were on the same frequency?

Who says the DHL611 crew didn't hear? Are you making an assumption or do you have a source for that?

Hearing another aircraft being told to descend doesn't, in and of itself, give the crew enough to go on.  The DHL crew followed the correct procedures by complying with the TCAS "Descend" command.

@GdD The DHL crew called out for TCAS-descent after the controller had twice asked the Bashkirian crew to expedite their descent. The second time he even relayed the position of the DHL to the Bashkirian(though it was incorrect). It was highly likely that it was the DHL aircraft that was referred to this situation. So, I inferred that the DHL crew didn't hear the ATC transmission.

@RalphJ The correct procedures in case of contradicting ATC and TCAS RA was established after this accident.Hence, this didn't restrict the pilot to comply with the TCAS RA. So, I was wondering why did the DHL crew descend even after the Bashkirian crew confirmed their descent with the ATC, that is if they heard the ATC transmission. Now if the DHL went ahead with their descend isn't highly likely that they didn't hear other transmissions.

Your inference is incorrect, according to the black box transcript the DHL crew did hear the transmissions. They did exactly as they were supposed to - ignored the radio and followed the TCAS instructions.

@GdD What source did you use for the cvr of DHL?

@Sreeram Here's the official report - it contains discussion of the DHL CVR and entirely agrees that the DHL pilots acted appropriately http://www.bfu-web.de/EN/Publications/Investigation%20Report/2002/Report_02_AX001-1-2_Ueberlingen_Report.pdf?__blob=publicationFile - see section 1.9.1 specifically

I have no idea @Sreeram, I read it years ago. google is your friend.

It wouldn't matter if they had.
The DHL611 crew had been trained to obey TCAS orders over ATC. This was fairly common, but not universal practice at the time. Their training was unambiguous, and stated that TCAS should be followed over ATC instructions. They had been trained that both aircraft would follow TCAS and avoid the collision, and had no reason to believe that wasn't the case: they didn't even necessarily know that BTC2937 was the aircraft causing their TCAS alert
The crew of BTC2937 hadn't been trained to follow these priorities, or became confused.
From the Wikipedia page about the incident:

The TCAS Pilot's Guide was ambiguous as to whether or not TCAS advisories should take precedence over ATC instructions.[BFU 14] This ambiguity was replicated in the Tu-154 Flight Operations Manual, which contained contradictory sections. On the one hand, chapter 8.18.3.4 emphasized the role of the ATC and describes the TCAS as an "additional aid",[BFU 15] whilst chapter 8.18.3.2 forbids manoeuvers contrary to the TCAS

Since that accident, it was made official procedure for all flights to follow TCAS, ignoring ATC when a TCAS RA is in effect.

Although all you say is true, "it wouldn't matter if they had" doesn't answer the actual question. The question was not "would that have prevented the crash?" but "Why couldn't the DHL611 crew hear the ATC transmissions for the Bashkirian 2937 crew?". I don't know whether it's true that the flights couldn't hear the instructions for the other flight, but this is the claim, which should be handled by the answer - by either refuting the claim or by confirming it and giving reasons (for why the instructions were not audible for the respective other flight).


text:
Is V(L/D)max equivalent to best glide speed regardless of weight, engine, height, etc.?
I've read Carson's paper on V(L/D)max, and while theoretically interesting, it does not seem to me to be useful in actually finding the V(L/D)max of an arbitrary aircraft, as it assumes knowledge of total parasite area (f) which can only really be calculated experimentally (and is very hard to calculate at that).
Another paper, by Russ Erb, claims that optimal glide speed, in the emergency section of the Pilot's Handbook for an aircraft, is equal to V(L/D)max for that aircraft.  This sounds wrong intuitively as it does not seem to take into account weight, air pressure, height, or other such variables.  As a math major, I am certainly suspicious of people who say "I'll spare you the derivations."
For an aircraft with an engine, such as a Cessna or a Bonanza, is best glide speed roughly equal to V(L/D)max?
I was told by an experienced pilot that

Vldmax at weight G = Vldmax at weight L * ( weight G / weight L )^0.5

This would seem to contradict the claim that V(L/D)max = best glide speed, as best glide speed (according to the Bonanza Operating Handbook, as an example), is constant.

Would that answer your question? By the way, the experienced pilot is right.

@PeterKämpf this is the best written synopsis I've seen yet, but it leaves me at the same impasse of not knowing how to discern form factor, roughness, or resulting total parasite area in order to calculate Cdo.

Calculation of $c_{D0}$ is an art in itself. You need to sum up all details to get close to a realistic value, or you get one from flight test which produces a wide scatter, so you need to measure multiple times. Sorry, there is no shortcut!

Is there an easy way to estimate using flight tests that recreational pilots could do? I'm trying to create an easy to use recourse for recreational pilots.

Please ask as a separate question. This is no question for the comments.

Weight does not vary that much in GA aircraft, so their POH just gives one value, for V(L/D)max likely average (for other V-speeds maximum or minimum depending on whether they are lower or upper limits). Transport aircraft where the difference between minimal and maximal weight is bigger have a table by weight (usually encoded in the FMS, so the value is indicated on the speed tape).

Awesome, thank you for that information. But wouldn't glide speed (calculated for engine being off) be different that V(L/D)max (engine on)?

I read that unless otherwise stated all GA POH values are for case of biggest allowed max weight? For example Bonanza POH doesn't have V(L/D)Max explicitly stated but does give an altitude/gph graph from which I can deduce speed for greatest mph/gph, and I assume that's for Max allowed gross weight.

@MaxvonHippel if your engine is on, you're not gliding. Because the engine is producing thrust (either positive or negative), it will change the range from a pure glide.

A few questions here, starting with parasite drag.  Here, experimental measurements in a wind tunnel would be helpful, as the old standby graph of induced lift going down and parasite lift going up with speed is pretty generic.  However, after looking at the PBY-3 Catalina and where they mounted the props (and flew it as a long distance patrol aircraft), one may conclude the lions share of drag is induced, particularly at lower GA speeds.
Potential energy (altitude, glider fuel) = m×gravity×height.  One can see this increases linearly with weight.  Speed increase needed to lift (at constant optimal AOA) a given weight increase is the SQUARE ROOT of the weight increase.  Drag produced by this speed increase is speed SQUARED.  This produces a linear relationship between gliding distance gained from increased weight compared with gliding distance lost from increased INDUCED drag.
Increased speed will produce a minor increase in parasite drag.  So, efforts to quantify this would focus on the drag coefficient of the prop, fuselage and tail. Here you're in luck as all studies are done at optimal WING AOA.
Keep in mind Vbg is based on Indicated Airspeed, so one need not worry about pressure or altitude.  So, for the practical GA pilot, Vbg will be fairly constant within the given safe weight range of your aircraft (but could be calculated while you do your gross weight and CG location work pre-flight), cargo carriers need consult the POH as Vbg will vary greater with a wider weight range.
Now, the other factor for Vbg is wind speed.  Here greater weight is advantageous for wind penetration.  Hence nature's inexorable millions of year process of trial and error has produced the heavy, fast high aspect ratio albatross to easily glide 1000s of miles on the wind.  Glider pilots add ballast under windy conditions, while the lighter wing loaded, slower vulture delights in riding the thermals.  Glider pilots may choose to lighten ballast under those conditions.
However, if wind is a factor, best glide slope (from best glide speed) can be determined just like in a landing, by observing how a fixed object in the distance moves in your windscreen.  At Vbg it will rise the slowest.  And landing is what you will be doing soon.

"Potential energy (altitude, glider fuel) = m×gravity" I'm quite sure you did not intend to write $E_{pot} h = m \cdot g$, but rather  $E_{pot} = m \cdot g \cdot h$

Noted and edited, thanks.

According to the FAA's "Best Glide Speed and Distance" handout provided by the General Aviation Joint Steering Committee ("GAJSC"), on most airplanes, the best glide speed is halfway between Vx and Vy. See Exhibit 1

Answers like these are very approximate, though.  Where I got stuck was trying to find a way to calculate the exact correct speed, not an estimate.  But getting the exact speed required surface roughness and wetted area, and I don't think I have any justifiable chance of really calculating either ....

… and yet this makes absolutely no sense. Note that there are two best gliding speeds—speed for best gliding distance and speed for best gliding time. The best gliding time speed is $V_y$. The best gliding distance speed, is always higher (and how much higher depends on weight).

@MaxvonHippel, the answer is not just approximate, it is clearly wrong.

What is wrong about it? The FAA document seems pretty straight forward. I just looked at a few POHs and the recommended engine failure speed by the manufacturer is approximately half-way between Vx and Vy.

@Devil07 you may likely be right in your interpretation of the FAA document, but there's a good chance (I think) that the FAA document in this case is wrong.  The math involved in finding this speed is really complex, and I have a hard time believing any "rule of thumb" like that could ever be any good.  That said, I'm a mathematician, not a pilot.

@MaxvonHippel Wetted area could be determined from a 3-view drawing of the aircraft. Surface roughness is a function of the finish of the aircraft, when it was last washed, and how many insects have splattered upon it since. Statistics play the dominant role here.

@Devil07 Vx will be affected by weight too.  53 knots would be a little close to stall for a heavy Cessna 172.  Note, at Vx, to get maximum climb per distance, we squeeze a little more Coefficient of Lift out of our wing by increasing AOA, using excess power to balance extra drag. As we get heavier, published Vx gets closer and closer to stall speed.  Safety margin is important with slow flight.  55 knots sounds more like it.   At Vy, we more efficiently go higher and farther in the same amount of time.


text:
Why does the radome on the AWACS rotate?
I'm not sure I understand why the radome on the AWACS aircraft is so large, and could somebody explain the design and why it has to rotate?

Basically, the radar antenna of the AWACS system is just like this (source):

Rotating waveguide antenna (picture source)
The round shape is only an aerodynamic fairing. Proof:

Boeing E-3A AWACS cutaway (picture source)
A surveillance antenna can also be fixed. Electronic beam steering helps to view a sector of approximately ±60°, but in order to get a 360° sweep the airplane needs to fly circles. Beam steering is also used on the rotating antenna to rapidly switch between several targets, so this is not unique to a fixed antenna:

Pakistani AWACS based on EMB-145 (picture source)

The alternative would be to have a stationary dome with the radar rotating inside. The Russians did that for their Il-76 AEW aircraft, this is the result:

This dome is noticeably thicker than that of the E-3 because there has to be space for the antenna inside the dome.
For the E-3, the outside surface of the antenna is also the outside surface of the dome (specifically, the white band of the dome), meaning the dome can be thinner.
The width of the dome is determined by the width of the antenna. The wider the antenna, the higher the resolution, so you want the largest antenna you can install.

In short: because it covers a full 360 degree area.

Mounted atop the aircraft fuselage in a rotating dome, the AWACS
  S-band (E-F band) surveillance radar is able to survey, in 10-second
  intervals, a volume of airspace covering more than 200,000 square
  miles (500,000 square km) around the AWACS, or greater than 250 miles
  (400 km) in all directions

If the radome did not rotate it would only cover the area in the direction the array was pointed (tangential to the stripe). Most similar radomes rotate, although some are enclosed so you may not see the rotating device.
There are also ways to do it with out a rotating array.

I personally don't get it. couldn't you rotate the array while not rotating the dome?

@Federico: You could. If the dome doesn't rotate, however, you need to make it a little larger (generally adding more drag) to leave clearance for things to rotate inside it. The exterior rotating also means the wear on the radome (and its coating) is distributed more evenly, which will generally reduce maintenance a bit as well.

Good answers above.
I just want to add that the planar arrays do not need to fly in circles (or rotate) to provide 360 degree coverage. The beams don't point solely perpendicularly from the radar on either the E-3 (rotating planar array) or E-7A (fixed planar array). They're electronically scanned:

A typical face will cover a 100-120 degree swath of the sky in front of it (a "two-sided" planar radar will cover 200-240 degrees). For fixed/longitudinally installed radars, the main arrays face sideways, and the other 160-120 degrees are often (but not always) covered by smaller radars that face forward and/or aft. These may have less power-range than the primary arrays.

[Boeing E-7 airborne early warning and control aircraft. Credit: Boeing.]
Example: the E-7 above has four main radars, two pointing left/right, two pointing fore/aft:

The 10.8 m long by 3.4 m high antenna assembly incorporates 7.3 m long
  by 2.7 m high Side-Emitting Electronic Manifold array, with the top
  hat supporting array providing 120° coverage on port and starboard
  side, while the top hat array itself provides 60° fore and aft, thus
  providing a complete 360° coverage.
  [Wiki. Sorry, I couldn't find an illustration/cutaway.]

So fixed/longitudinal arrays do not necessarily need to fly in constant circles to provide 360 degree coverage. (Note that this is different from saying that the quality/range of coverage is uniform for all bearings. This also isn't saying that AEWC don't fly circuits. The actual tracks can vary and take into account friendly forces and the anticipated threat direction to best situate/point the faces while minding your own security.)

Oh, come on. We both know that a 90* viewing angle is impossible. So please don't imply this.

@PeterKämpf - Do you mean 180°? Because I agree that's nigh impossible. But ~90° isn't that hard. The Burkes have a 4-face SPY-1 radar (so too several other AAW DDGs/FFGs/CGs); each face covers ~90°. The Zumwalt and Ford each have a 3-face DBR; each face covers ~120°. This is TPY-2 (approx coverage, 1 face): https://www.38north.org/wp-content/uploads/2016/03/Fig1_THAAD1.jpg

I did not talk of a viewing sector but a viewing angle. As you confirm, a ±60° viewing angle is about the practical limit.

@PeterKämpf - All the numbers I used reference total coverage, not half angles. Eg, "120 degree swath of the sky in front of it" obviously does not refer to a half angle---a 240° FOV from a flat surface would be nonsensical :)

The radome on the AWACS is NOT the black bit. The radar is mounted on the long faces of the metal bit on the diameter, and 'sprays' radar out through the aerodynamic shaping of the black part. Since the radar beam is directional, like most radar beams, it has to be rotated to get 360d coverage.

You answer is good and may be enhanced by adding references and maybe an exploded view of the AWACS.


text:
How do we find the breaking point of an old braced wing?
I was curious about how to find the maximum g's an old plane like the Spitfire (c-wing) could endure, given all realistic factors. Since the Spitfire's wing, in particular, was quite thin and braced with wood for most of its variants how much positive and negative force could it withstand?

Not sure what you mean by "old braced wing", the Spitfires were full cantilever wings from the first prototype 300. From this link:

This link references the original Spitfire specification (without any further references to them):

5 Structural Strength
(a) The strength of the main structure when carrying the load specified in paragraph 3, plus 100 lb shall not be less than as specified hereunder ——
Load factor throughout the structure with the centre of pressure in its most forward position 9.0.
Load factor for wing structure with the centre of pressure in its most backward position in horizontal flight 6.0
Load factor in terminal nose dive 1.75
Inverted Flight
(1) Load factor at incidence corresponding to the inverted stall and with C.P. at 1/3 of chord 4.5
(2) Load factor at incidence appropriate to steady horizontal inverted flight and at the maximum speed of horizontal normal flight 4.5

Most WWII planes still flying are not stretched to the limit regarding g's, to keep exceed the fatigue life. I doubt any current owner would like to test what load the wings are up to at present.

No worries, feel free to accept the answer if you are satisfied with it.

Of course, my bad


text:
Why didn't Air India always fly DEL-SFO over the Pacific?
I read a 2016 article that said Air India broke a record for the longest flight (distance) by flying from New Delhi to San Francisco over the Pacific rather than a polar/Atlantic route. The total flight time was shorter because of the jet stream.
Why didn't they always do this?

In addition to the other answers, it's worth pointing out that the jet stream does not stay in a constant location above the Earth, but shifts and meanders over the course of weeks and months.  Here's a great video from NASA showing these shifts over a 30-day period:

The Pacific route would only be advantageous if the jet stream was relatively far south in its meanderings.

Do airlines change routes ~daily to optimize for this?

@DavidEhrmann:  I don't know for sure, but it wouldn't surprise me if that was true.

The great circle (shortest path) between DEL and SFO goes nearly straight north then nearly straight south (slightly westerly). It's super close to a route where you would go straight north, then straight south. For instance, I plotted DEL to DEN (Denver-CO), and there we have a straight north route.
The fact is, often times the shorter distance (great circle) actually beats the Pacific route, and the jet stream isn't straight from the west to the east. It does shift to the north and south in many places.
It might be just better to plot a DEL-SFO route where the aircraft goes mostly north but picks up a northeast jetstream in the beginning and then picks up a southeast jetstream in the end. I've seen jets flying in the northern USA on a heading 040 (more north than south) with a 100+ knots tailwind.

North then south. Amtrak does that too, that's why the Coast Starlight #11/14 are not adjacent numbers.  All eastbounds are even.  Seattle-Oakland is #11 where it then turns eastward to L.A. as timetable #12 (ticketed as #11).  Railroads only use 2 compass points systemwide. The end of the Central Pacific RR was the San Franciso Ferry Terminal. This became the West Pole on CP successors. Thanks, Lincoln.

The polar route is actually a shorter distance. So, in the absence of winds (and in the absence of political conditions preventing you from overflying certain regions,) the polar route is faster.
The jet stream moves around and its average location and strength vary seasonally. Even within a season, though, its position and strength can vary significantly even from one day to the next.
Taking the Pacific route instead of the polar route adds quite a significant amount of distance to the DEL-SFO flight. As such, it only makes sense to take that route when the jet stream is strong and located conveniently for where you're trying to go. If the jet stream is weaker and/or heading the wrong way for your route, taking the polar route will be faster.
In the absence of wind, the only downside to taking the polar route over the Pacific route is that, if you have to divert mid-flight, you'll end up in some frozen wasteland in Russia, Canada, Svalbard, or Greenland, rather than some tropical island in the Pacific.


text:
What are the aerodrome services SRE and CEV?
eAIP in France list two services on AD-2 (aerodromes) for which I have no clue what they stand for. They are not known to AIXM neither.

SRE found on eAIP of aerodrome LFOA
CEV found on eAIP of aerodrome LFBD

Any idea what these services are? Thanks a bunch!

There are two types1 of flight activities in France, civil and military, they are clearly separate:

Civil aircraft activity is known as CAG, Circulation Aérienne Générale / General aircraft traffic. CAG documentation is found in the French AIP published by SIA, the one you looked at. This is the aeronautical information compliant to ICAO recommendations, which is used by all aircraft in France.

Military aircraft activity is know as CAM, Circulation Aérienne Militaire / Military aircraft traffic. CAM is specific to military and State aircraft activities, and therefore is not to be used by any civil traffic. CAM is supervised by DirCAM (CAM Department) and documentation is found in the French MilAIP (e.g. this high altitude military navigation chart -- Note the bicolor rectangles, the points near the borderlines, were the traffic can be switched between CAM and CAG). DirCAM can provide common information through the SIA AIP too.

CEV and SRE are ATC services restricted to CAM aviation. That's why you don't see the relevant details in the SIA AIP. The related procedures are available in the MilAIP. Description of them follows.
Contrary to what is observed in some countries (e.g. USA), aerodromes are never shared between civil and military flights. Military have their own air bases which are inaccessible to civil flight (unless exceptional circumstances, including emergencies), except State agencies.

CEV: Centre d'essais en vol (flight testing center)
Tests in flight are under the management of a State administration which performs these flights as CAM traffic, both for civil and military tests.
This administration has been known as Centre d'Essais en Vol (CEV), but has been reorganized a few years ago and is now part of Direction Générale de l'Armement (DGA), the French Defense Procurement Agency.

DGA-EV badge. Source
For its test flights, DGA-Essais en Vol (DGA-EV) uses the ATC "CEV service". Only selected ATC centers provide a support to DGA-EV on a specific frequency.
DGA-EV can be seen like an operator, performing only flight testing with specific privileges. You may read about DGA / EV in this Wikipedia article (Google Translate).
One well known CEV aerodrome has been Brétigny CEV. Brétigny was a flight testing aerodrome near Paris, collocated with BA 217. More on CEV history in the French document (pdf, no translation available).
You mentioned LFBD, Bordeaux-Mérignac. There are at Bordeaux some DGA aicraft used for flight testing, e.g. this Fokker 100:

DGA-EV Fokker 100 F-GPXL. Photo by Guillaume Carré at Flickr
It seems the tests are related to the missile visible under the tail and / or the Thales pod.
There are flight testing ATC operators at specific positions in the ATC room, which task is to support such aircraft. Regarding the MilAIP documentation for LFBD:

MilAIP for LFBD. Source
You can see there are two Special Controlled Temporary Airspace used for flight testing, with the corresponding CEV callsign and the schedule for activation (7 am to 4 pm, business days). In France, S/CTA are controlled by military operators. (There is a third S/CTA but under the control of Cognac. I mention it just because Bordeaux and Cognac are well-known, but not for their CTA.)

S/CTA Bordeaux. Source

SRE: Surveillance Radar Element
ATC service used for approach to military bases using a Search Radar Equipment (SRE) renamed Surveillance Radar Element as noted by ymb in his answer
A SRE is a long range panoramic radar, part of a Ground Controlled Approach (GCA) system. The GCA is composed of two segments:

One used before the actual approach, using the SRE to determine the position of the aircraft and guide it to the Initial Approach Fix (IAF) where the PAR radar takes over.

The Precision Approach Radar (PAR) segment where the PAR is used to guide the aircraft to the runway threshold.

Difference between a SRE radar (left) and a PAR radar (right):

SRE and PAR systems. Source: Left - Right
As you mentioned LFOA, below is the PAR procedure at Avord base (BA 702 / LFOA) looks like this:

LFOA, PAR procedure. Source
The PAR approach above for example requires a Tacan transponder in the aircraft, something civil aircraft don't have (they have the DME portion but miss the bearing determination one).
See also: What is a SRE approach on PPRuNe. More here in French (Google Translation).

Note1: To be exhaustive, there are two additional types of traffic: CER and COM:

Circulation Essais et Réception, used by aircraft manufacturers for prototype testing and customer acceptance flights.

Circulation Opérationnelle Militaire, used by military for actual operational missions.

That's interesting that France does not provide PAR to civilian aircraft at all -- my understanding is that PAR service at US military bases is available to civil aircraft authorized to use the base (which can be "all of them" at joint civ/mil facilities such as KNYL)

@UnrecognizedFallingObject: Military air bases are for "CAM" only, not open to "CAG". Only civilian allowed are CEV flights. Except emergencies of course, which happen from time to time (Space Shuttle was allowed to land at Istres, but it was a specific agreement with US personnel on the base). There are no jointly managed airspaces, only military representatives at civil ATC enroute centers to facilitate CAM in CAG airspaces.


text:
"END PART" Statement in NOTAM
Here's yet another installment of "how fun it is to parse NOTAM". ;-)
Statements like "END PART 2 OF 2" are quite common in the E) item of NOTAM, however, the following has triggered a red light on my parser:
D3616/22 NOTAMN
Q) EDGG/QRTCA/IV/BO /W /000/100/5003N00804E012
A) EDGG PART 2 OF 2 B) 2211160800 C) 2211181800
D) NOV 16 0800-2200, NOV 17 0500-2200, NOV 18 0500-1800
E) - FLTS CONDUCTED ENTIRELY UNDER IFR DEP/DEST FRANKFURT/MAIN EDDF,
FRANKFURT-HAHN EDFH AND RAMSTEIN ETAR (CHANGE PROCEDURES ARE NOT
ALLOWED) WHICH FULFIL THE ICAO STANDARDS LAID DOWN IN ANNEX 17
(SAFEGUARDING INTERNATIONAL CIVIL AVIATION AGAINST ACTS OF UNLAWFUL
INTERFERENCE) OR REGULATION (EC) NO. 300-2008 OF THE EUROPEAN
PARLIAMENT AND THE COUNCIL OF 11 MARCH 2008. THE TERM -CHANGE
PROCEDURES- REFERS TO ALL FLTS THAT ARE CONDUCTED WHOLLY OR PARTLY
UNDER VISUAL FLIGHT RULES (Y AND Z FLIGHT PLANS).
TRAINING FLIGHTS, PHOTO AND CALIBRATION FLIGHTS (INCLUDING UNDER
INSTRUMENT FLIGHT RULES) ARE NOT ALLOWED.
PRIOR ENTERING, LEAVING OR TRANSITING THE AIRSPACE ALL AUTHORISED VFR
FLTS SHALL REPORT TO THE POLICE OF HESSEN. THE PROCEDURES TO BE USED
FOR THIS WILL BE COMMUNICATED BY THE POLICE VIA THE APPROPRIATE
CHANNELS. ALL AUTHORISED VFR FLTS SHALL MAINTAIN CONTINUOUS
AIR-GROUND VOICE COMMUNICATION WATCH ON FREQ 135.600MHZ (POLICE INFO)
WHILE FLYING WITHIN THE RESTRICTED AREA. CROSSING APPROVAL IN
CONJUNCTION WITH SECTION 17 LUFTVO WILL NOT BE GRANTED.
F) GND G) FL100
END PART 2 OF 2
CREATED: 15 Nov 2022 15:42:00
SOURCE: EUECYIYN

In this case it's not part of the E) item, but squeezed in after the G) item and the meta data CREATED and SOURCE.
There is no mention of "END PART" in Doc 8126, so the only place I see it fit is the free form E) item. However, after grepping a few thousand NOTAM, I couldn't find another example which contains both "END PART" and a G) item.
I assume, it's been misplaced in this case. Am I right?
Thanks for your help!

@Yuri Sucupira Shamelessly pinging you since you're a former NOF.

It is not part of any particular item. Rather it is a general informational pointer than the NOTAM is so long it has spread across two separate issuances.
From the FAA's Defense Internet NOTAM Service I pulled this text:

D3616/22 NOTAMN
Q) EDGG/QRTCA/IV/BO /W /000/100/5003N00804E012
A) EDGG PART 1 OF 2 B) 2211160800 C) 2211181800
D) NOV 16 0800-2200, NOV 17 0500-2200, NOV 18 0500-1800
E) TEMPO RESTRICTED AREA EDR RHEINGAU ESTABLISHED 495537N 0075944E -
CLOCKWISE ALONG THE ARC OF A CIRCLE 5NM AROUND 500000N 0075600E -
500423N 0075215E - 501023N 0080916E - CLOCKWISE ALONG THE ARC OF A
CIRCLE 5NM AROUND 500600N 0081300E - 500131N 0081627E -
495919N 0081013E - 495936N 0081003E - 495728N 0080400E -
495708N 0080400E - 495537N 0075944E.
ALL FLTS ARE PROHIBITED IN THE RESTRICTED AREA EDR RHEINGAU. THE
FOLLOWING FLTS ARE EXEMPTED FROM THE FLIGHT RESTRICTIONS:
- FLTS BY STATE AIRCRAFT RELATED TO THE G7-CONFERENCE AT ELTVILLE,
- FLTS OF THE GERMAN ARMED FORCES,
- FLTS OF THE UNITED STATES ARMED FORCES WITH DEP/DEST WIESBADEN
ETOU,
- ACTUAL POLICE MISSION FLTS AND FLTS ON BEHALF OF THE POLICE
- FLTS ON RESCUE AND DISASTER PREVENTION MISSIONS,
- AMBULANCE FLTS,
- FLTS BY MODEL AIRCRAFT AND UNMANNED AIRCRAFT SYSTEMS AT A DISTANCE
MORE OF THAN 1NM FROM 500235N 0080247E, TAKING ACCOUNT OF THE
REGULATIONS OF SECTION 21H OF THE GERMAN AVIATION REGULATION LUFTVO
AND UNLESS THEY DO NOT FLY ABOVE AN ALTITUDE OF 120M ABOVE GROUND
END PART 1 OF 2
CREATED: 15 Nov 2022 15:42:00
SOURCE: EUECYIYN

D3616/22 NOTAMN
Q) EDGG/QRTCA/IV/BO /W /000/100/5003N00804E012
A) EDGG PART 2 OF 2 B) 2211160800 C) 2211181800
D) NOV 16 0800-2200, NOV 17 0500-2200, NOV 18 0500-1800
E) - FLTS CONDUCTED ENTIRELY UNDER IFR DEP/DEST FRANKFURT/MAIN EDDF,
FRANKFURT-HAHN EDFH AND RAMSTEIN ETAR (CHANGE PROCEDURES ARE NOT
ALLOWED) WHICH FULFIL THE ICAO STANDARDS LAID DOWN IN ANNEX 17
(SAFEGUARDING INTERNATIONAL CIVIL AVIATION AGAINST ACTS OF UNLAWFUL
INTERFERENCE) OR REGULATION (EC) NO. 300-2008 OF THE EUROPEAN
PARLIAMENT AND THE COUNCIL OF 11 MARCH 2008. THE TERM -CHANGE
PROCEDURES- REFERS TO ALL FLTS THAT ARE CONDUCTED WHOLLY OR PARTLY
UNDER VISUAL FLIGHT RULES (Y AND Z FLIGHT PLANS).
TRAINING FLIGHTS, PHOTO AND CALIBRATION FLIGHTS (INCLUDING UNDER
INSTRUMENT FLIGHT RULES) ARE NOT ALLOWED.
PRIOR ENTERING, LEAVING OR TRANSITING THE AIRSPACE ALL AUTHORISED VFR
FLTS SHALL REPORT TO THE POLICE OF HESSEN. THE PROCEDURES TO BE USED
FOR THIS WILL BE COMMUNICATED BY THE POLICE VIA THE APPROPRIATE
CHANNELS. ALL AUTHORISED VFR FLTS SHALL MAINTAIN CONTINUOUS
AIR-GROUND VOICE COMMUNICATION WATCH ON FREQ 135.600MHZ (POLICE INFO)
WHILE FLYING WITHIN THE RESTRICTED AREA. CROSSING APPROVAL IN
CONJUNCTION WITH SECTION 17 LUFTVO WILL NOT BE GRANTED.
F) GND G) FL100
END PART 2 OF 2
CREATED: 15 Nov 2022 15:42:00
SOURCE: EUECYIYN

You can see that Items Q through D are duplicated at the beginning of each NOTAM, except that in the first NOTAM Item A is "EDGG PART 1 OF 2" while in the second NOTAM Item A is "EDGG PART 2 OF 2."

Great you found these examples. It's fascinating how "creative" some NOF are in adding stuff nowhere close to Doc 8126. Knowing that, I'll just find and deal with such part markers about anywhere in the payload before parsing the rest... which should take care of it once and for all. Thanks a lot!


text:
Is there a specific form or format for a written report of a deviation, submitted per 91.3(c)?
14 CFR 91.3(c) mentions "(...) upon the request of the Administrator, send a written report of that deviation to the Administrator" - what does a report like that look like? Is it as simple as a "To whom it may concern" letter with a few paragraphs about the deviation? Or are the forms involved, etc., etc. Any examples?


text:
Why does the attitude indicator gyro not precess the same way that a directional gyro does?
The directional gyro needs to be realigned every so often, but the attitude indicator does not, and I have a hard time finding why.

knowing which brand/model instruments you are talking about might help us answering you, as not all are guaranteed to be the same.

... I don't have a specific make and model in mind, let's say 'traditional' vacuum-driven ones. PHOAK specifically calls out the directional gyro, but does not mention the attitude indicator.

Are these truly just gyros? Because the typical reason is that your attitude gyro has an absolute reference with which another instrument can be used (such an accelerometer, for example) to correct long-terms errors against: gravity.
Your directional gyro doesn't have such a thing unless it also involves a compass.

@DKNguyen I think the OP is referring to old school AIs & DGs from back before they were known as steam gauges. There was a time before we had accelerometers, magnetically slaved instruments, or flux gates. Six-packs were powered by pitot-static systems and vacuum pumps solely. Some even dispensed with vacuum pumps and were powered by Venturi tubes. The backup instruments of some glass panel trainers still rely on old-school technology. They are not all Aspen, glass or evening electric driven like your 1970s Turn Coordinators. These aircraft are still flying. Especially in the training fleets

@DeanF. Even so, I imagine it would be much easier to gang an attitude gyroscope to a weight than to mechanically link any kind of absolute heading reference to a heading gyroscope.

@DKNguyen - I am really not sure what you mean by your comments. Of the aircraft I rent, those with accelerometers, HSIs that are slaved to magnetometers or glass cockpits, rarely to never require the need to periodically adjust or align the DG or AI after initial alignment. However, the Cherokees, Arrows, C150s, C152s, and C172s that are old enough to have nothing more advanced than a G530 or less in them, most of them have AIs and DGs that are solely powered by vacuum pumps. One C140 has a Venturi tube instead. There are no accelerometers nor magnetometers integrated into the six-pack.

@DKNguyen - That is why I made the point that there are a multitude of aircraft flying in the training fleet that would have their DGs and AIs as “truly just gyros”. Now, as previously mentioned, gravity and load due to things like centripetal force on gravity switches and pendulous vanes may effect AIs more than DGs to keep them from precessing in straight and level, unaccelerated flight. Yet, they are still just gyroscopic instruments.

Heading indicators can be slaved to a magnetic sensor giving them the ability to continuously self adjust similar to the attitude indicator. (More commonly found with the HSI style)

The self erection device in the attitude gyro that levels it when you start up on the ground also keeps it erect (its axis pointed at the center of the earth) when precession tends to send it off kilter during flight.
Air driven gyros use a pendulous vane arrangement that controls the exhaust ports for the air being sucked through, and which always work to keep the gyro aligned with vertical when stabilized in non-accelerated flight.  This system is imperfect, because the pendulous control system is influenced by accelerations and causes its own errors, but works well enough for light aircraft.

Precession and pendulous vanes operate on a scale magnitude of around a degree per minute, and maneuvers with significant acceleration last less than 1-2 minutes so the max error is limited by the slow response of the vertical correction. And the significance of the error is limited by the useful display resolution.

I am no expert. My understanding of the Gyroscopic Attitude Indicator is that it is free to move relative to the fuselage in all three axis of motion until you go past 60° in any of the directions of motion. No outside force is applied to the gyroscope until the mechanical limitations of the instrument are reached. Once the mechanical limitations of the instrument are exceeded, the attitude indicator may tumble.
In the case of the Directional Gyroscope, on the other hand, it is constrained to move freely only upon one axis relative to the fuselage. Movement upon the other two axis is possible, but more constrained due to mechanical limitations. When the fuselage reaches attitudes that will exceed those limitations, force will be applied to the gyroscope. That force will be translated to movement in the plane of motion displayed along the axis of freedom of movement. In other words, a pitching motion of the longitudinal axis around the lateral axis, will be translated into precession or yawing motion of the longitudinal axis around the vertical axis.

In the artificial horizon the spin axis of the gyro is tied by the earth's gravity to remain in the earth vertical. That's the reason why this gyro is also known as an Earth gyro. As John K said, this gyro uses a system of erection. Air driven uses pendulous vanes and electrical gyros use a system with electrical motors with gravity switches (with mercury) to orient and continuously maintain the axis to local vertical.
This type of gyro has two degrees of freedom. Those system are not free of errors. In air driven gyros for example, the pendulous system can give you false indications when doing manoeuvres. Basically there are acceleration and turniing errors.
Examples:
During an acceleration phase at constant altitude, the resetting principle of the artificial horizon results in the horizon bar indicating a nose-up attitud.
Following 180° stabilised turn with a constant attitude and bank, the artificial horizon indicates too high pitch-up and correct banking.
These errors are related to mechanical gyros. In the new electronic system these errors doesn't exist anymore
See this link to fully understand the erection system: https://www.theairlinepilots.com/forum/viewtopic.php?f=35&t=905&p=1204&hilit=artificial+horizon#p1204

"These errors are related to mechanical gyros. In the new electronic system these errors doesn't exist anymore".  That depends on the accuracy.  Differentiating drift from a slow banked turns is still tricky for an AHRS, particularly on the low-end without GPS aiding.

@Cody P, yes you are right, in purity all systems have errors, but from the pilot point of view I would say they are minimal compared to the old mechanical gyros.

Yes, I agree that especially from a pilot perspective theses errors are much smaller than for mechanical gyro, especially with GPS-integration on AHRS becoming more and more common.

Both attitude and directional indicator are using a gyroscope to remain stable inside the aircraft. This means that their orientation is not perturbed by the aircraft evolutions, the horizon of your AI will remain on the real earth horizon whatever the plane attitude and your DI will keep it's internal orientation constant thus helping you in a turn to evaluate your real heading.
On one hand your attitude indicator is aligned with the horizon and display your pitch and inclination. Those informations are only related to your airplane and gravity (normally the horizon is perpendicular to gravity). Most AI have mechanism that keeps them aligned with the gravity otherwise you might develop small error in your pitch angle due to the curvature of the earth on long trips covering large distances.
On the other hand the directional indicator should be aligned with the earth magnetic field to display your heading. Those informations are related to the airplane orientation and the magnetic field. And this field is rotating 15°/hour due to the earth rotation. This information has no other way to be transfered to your system than manually realign the display with a magnetic compass (or electronically in new ones).

... regarding the DG, it makes sense in the context of a cross country flight, what about - say an 1.5 hr flight of shooting local instrument approaches, where the aircraft operates within some 20 nm corridor between longitudes?

"Some AI have mechanism that keeps them aligned with the gravity" – I thought all AIs had such mechanisms. What's one that doesn't?

The gyroscope keeps an absolute orientation. Your aircraft is following the earth rotation but not the gyroscope. The fact that your flying on the same longitude doesn't change. Let's say you can be in space looking at the earth and gyroscope, 1h later the earth will have rotated 15° but the gyroscope on its surface will have kept the same orientation from your point of view

@terran Swett I've seen some old ones that you might now encounter in flight schools display for learning purpose that didn't had this, but they were from early ages of aviation ^^


text:
Where is an example of "foreign airspace designated in the United States" mentioned in 91.129?
Reading 91.129 regarding Class D ops and establishing communications, (c)(1) mentions:
"including foreign ATC in the case of foreign airspace designated in the United States"
Can anyone point to an example of such airspace?
Ref.: https://www.gleim.com/aviation/faraim/index.php?leafNum=91.129

The Sault Ste. Marie Airport (CYAM) is a Canadian airport with Class D airspace that extends into US territory:

Skyvector

The chart there shows the atc boundary running through the class D. Do you know how that is managed?

@TomMcW I would assume that the tower would be able to take handoffs from both ARTCC/ACC facilities, but I don't know for sure.

@TomMcW also possible: the airspace boundaries have different altitude restrictions, which would also deconflict.


text:
Can pilots take multitools on board in Canada?
Can pilots in other countries or Canada carry Swiss army knives onboard on commercial flights? Passengers are not allowed to do that in Canada.

Funny thing is, they often (always?) have an axe in the cockpit.

is that an international standard for axes to always be available?

I only found this: "FAA Section 91.513 states: “Each airplane accommodating more than 19 passengers must be equipped with a crash axe."

In Geneva you can even buy them as a passenger at the airport (after passing security). No problem, as long as the blade is shorter than 6cm.

In certain regions of Danish and Canadian arctic airspace the crew is required to carry a shotgun in case of polar bear encounter after a forced landing.

Axe, shotguns...some people take that zombie thing rather serious.

@pericynthion on a commercial flight or like those passenger planes of four people?

@Bianfable in Canada less than 6 cm is allowed now even for passengers.

Either Gerber or SOG, at one time, made a full-sized TSA compliant multi-tool. Good luck trying to get it through security. Probably more hassle than it’s worth. Even with the big red TSA-compliant logo embedded into the metal. Plus, it lacked any cutting tools (of course).

pilots are never allowed to have any kind of weapon on board. when pilots go to work they have to go security just like the passengers.
there has been accidents because of this.
https://en.wikipedia.org/wiki/Federal_Express_Flight_705#Flight_crew_and_hijacker
its maybe allowed when the total length is smaller then your hand but i`m not sure if this rule applies to pilots.

Eh....that’s not exactly true.  Some company SOPs do allow a flight crew to be armed, if needed.

In the US, pilots can participate in the Federal Flight Deck Officer program and are allowed to carry weapons on board.

And by weapons, Bianfable means firearms. Guns, that is. There are companies that even make pilot flight bags in which to carry them.

When is something a "weapon", and not simply a tool or random object?  I think many pilots carry briefcases/flight bags, yet these can make quite handy improvised weapons.  And then there's that axe in the cockpit :-)